1. Field of the Invention
The invention relates to assistance with navigation or with piloting, with a view to directing a mobile towards a target which can move or more generally towards a target whose exact position is not known a priori. This navigation or this piloting is referred to hereinafter as "relative navigation"; the mobile will be referred to as the "hunter", the objective of the hunter being the target.
The applications envisaged here are in particular the following:
landing of a helicopter or of an aircraft on a ship, or an oil platform, PA1 space rendezvous, PA1 rendezvous between surface ships or submarines, PA1 pursuit of one vehicle by another, PA1 in-flight refuelling, PA1 motion of vehicles in formation while remaining a specified distance from a leader, PA1 motion of vehicles towards a beacon at sea (for ships) or on the ground (for helicopters or terrestrial vehicles) although the position of the beacon is not known a priori, PA1 motion towards points whose positions are known with respect to a beacon although the position of the beacon itself is not known.
The applications envisaged are applications in which the accuracy of positioning is a predominant parameter.
2. Discussion of the Background
The systems proposed hitherto for these applications are not sufficiently accurate or demand calculating powers which are too large to allow real-time applications with sufficient accuracy. For the case of aircraft landing on an aircraft carrier, it is understood that the calculation must be performed in real time with great accuracy and a high rate of information refresh.
The following procedure could be used: a satellite-based positioning receiver placed on the target sends its position to the hunter by radio. Another receiver on the hunter calculates its position and performs a subtraction between the two calculated positions so as to determine the components of a vector joining the mobile to the target. The pilot of the mobile uses these components as an aid for steering towards the target.
This solution is not satisfactory owing to the uncertainties which affect the position information calculated by the receivers. It is recalled that the positions are calculated with a certainty tied to the clock fluctuations of the signals transmitted by the satellites.